how do I get blender to stop rounding up my dimensions?
By default blender uses metric measurement system with Unit System set to None and rounding to 3 decimal places wich best suited for real world objects:



If you using Impereal Unit System rounding wich default to Feet rounding can be from 0 to 3 decimal places. This can be inconvenient when manipulating with a gizmo.



In this case, you can use Length in Thou wich meant "Thousandth of an inch":



For more complex cases: work with micro or macro objects - suitable overriding of Unit Scale: